Cities are an often overlooked as being a major contributor to climate change. Yet their diversity has made it hard to assess how far they can cut their emissions.
Moreover, efforts to tackle their emissions, such as those from urban transport, often come with trade-offs in terms of costs and co-benefits from cleaner air or health.
In our new study, published in Nature Sustainability, we conducted a comprehensive analysis of transport policies in 120 cities, spanning five continents.
We found that the cities could cut carbon dioxide (CO2) emissions by a combined 22%, without cutting residents’ quality of life measured via an aggregate, monetised metric.
In individual cities, we found that a combination of policies, such as fuel taxes, public transport improvement and urban planning, could reduce transport CO2 by up to 31%.
Cities in climate policies
Cities bear a major responsibility for climate change, as they account for 70% of global emissions.
They can also play a key role in implementing climate action at the local level. Many cities have set ambitious climate goals, with members of the Global Covenant of Mayors city network, for instance, aiming to reduce their emissions by 66% by 2050.
Urban transport, in particular, is an important sector, representing 8% of global emissions alone. This also tends to be an area where cities have the ability to act.
Yet, quantifying the aggregated potential of cities to mitigate transport emissions has proven challenging. Indeed, the impacts of city-level policies depend on the unique characteristics of each city, such as urban spatial organisation and existing infrastructure.
On the other hand, detailed city models applied to case-study cities are difficult to generalise, since the scientific literature is fragmented and biased toward larger cities and developed countries.
Exploring strategies
Using an urban simulation model, we estimated the aggregate potential for 120 cities on five different continents to reduce their urban transport emissions.
We also considered the impact of such climate actions on inhabitants’ quality of life, through housing and transport prices, local taxes and health co-benefits related to transportation. This included those related to cleaner air, reduced noise, reduced traffic accidents and increased physical activity due to active transportation modes.
The 120 cities are home to 525 million inhabitants, or about 20% of the total global population that lives in cities larger than 300,000 people.
To calibrate the model on each city, we relied on spatially explicit socio-economic data that we collected through web-scraping of local websites, as well as data on local transportation systems that was provided by Open Street Map, Google Maps and Baidu Maps.
Our study explores four main types of complementary strategies that could help reduce transport-related emissions in cities: taxation of polluting vehicles; incentives to use vehicles that consume less fossil fuel; investment in public transport; and urban planning policies that restrict urban sprawl.
For each of these strategies, we examined examples of public policies that can be implemented at local level. For example, to improve public transport, one possibility is to set up a bus rapid transit system on dedicated lanes.
Other examples include that urban planning can involve limiting new construction away from public transport stations. Polluting vehicles can be taxed by raising fuel prices or by introducing local congestion charges.
Finally, the use of more efficient vehicles, such as electric cars, can be encouraged by a combination of subsidies and bans on the most polluting vehicles in urban centres.
Comparing local policies
Our findings suggest that a combination of these policies could reduce overall transportation GHG emissions by up to 31% in 15 years, across the 120 cities studied.
Policies implemented individually could mitigate emissions by 4% to 12%, depending on the policy considered.
These results are in line with the scientific and “grey” literature on the topic, which has shown that urban transport emissions could be mitigated by 20% to 25% through a combination of urban planning and technological solutions.
The impact of a given policy varies according to the city in which it is implemented. For example, in the majority of South American cities studied, the introduction of new public transport lines would be particularly beneficial, our results suggest.
Given the relatively high population density and underdeveloped public transport systems in these cities, our simulations indicate that the implementation of new public transport lines could potentially reduce emissions by up to 21% and 26% in Brazilian cities such as Goiânia and Belém, respectively.
In Europe, taxing fuel prices appears to be more effective, primarily due to the generally well-developed public transport networks available in European cities. For instance, a fuel tax would lead to a 7.5% reduction in transport-related emissions in Barcelona, we found, while the impact would be only 0.6% in Atlanta (USA), where alternatives to private cars are less readily accessible.
Simultaneous implementation of multiple policies can have a particularly significant impact, our results show. Combining taxes on polluting vehicles with public transport development could result in substantial emission reductions, as could promoting public transport alongside measures to control urban sprawl and increase population density near railway stations.
For instance, in Lille (France), implementing policies to control urban sprawl, tax polluting vehicles and develop public transport concurrently would potentially reduce transport-related emissions by almost 24%, compared to reductions of 9%, 4%, and 7%, respectively, if each policy was implemented individually.
An example of the differing impact of public transport development on CO2 emissions after 15 years can be seen in the map below, with purple circles showing cities that could achieve a more than 10% saving, blue showing 5-10%, green 1-5% and yellow less than 1%.
Variation in transport-related CO2 emissions
Inhabitants’ quality of life
Assuming that these policies are fully financed locally by a tax, our study also estimates their impact on the material conditions of residents and on their health.
We analysed the impacts of urban transport emission reduction policies on a range of factors linked to quality of life. In terms of income, for example, building locally financed public transit lines increases local taxes, while taxing polluting vehicles reduces them. We also looked at transportation costs, average housing prices, air quality, noise pollution, road accidents and the health benefits associated with “active” mobility (walking or cycling instead of driving).
Depending on the city, these impacts can be positive or negative overall. A fuel tax or the opening of new public transport lines would be expected to improve air quality, reduce noise pollution and the number of road accidents. More efficient vehicles improve air quality and reduce the household transport budget – even if their impact in terms of road accidents remains unchanged.
On the other hand, urban planning that limits urban sprawl can contribute to higher housing prices and the introduction of public transport lines can sometimes prove extremely costly.
To facilitate comparison, we expressed these variations in monetary terms, creating a composite indicator of welfare that encompasses all dimensions of residents’ quality of life mentioned earlier, as shown in the figure below.
Our study reveals that, in all cities examined, there are policy combinations that can effectively reduce emissions while improving overall well-being.
Most importantly, if, in each of the 120 cities of our sample, instead of applying all the policies that we considered, we choose to apply only policy combinations which do not reduce our monetised measure of welfare, we find that we can reach in total a 22% reduction in urban transportation GHG emissions in 15 years.
This means that most of the emission reductions that we simulate in our study can be reached without affecting residents’ quality of life in any of the cities that we considered.
While 22% is not sufficient, in itself, to reach carbon neutrality, we only analysed four simple and generic policies. Specifically designed and optimised policy portfolios for each city could reach larger emission reductions.
Climate governance and research
As numerous protests worldwide have demonstrated, public policies aimed at reducing emissions must also positively impact residents’ quality of life to gain acceptance.
In all the cities that we studied, we found that it is possible to combine reduction of GHG emissions and the enhancement of quality of life, through well-adapted policy choices.
In order to achieve this, the set of policies needs to be tailored to each city’s specificities, however, with strategies which cannot necessarily be directly transposed from one city to another. In our city sample, the emission reduction that can be reached – even with a generic policy toolkit – is also significant.
Cities are frequently overlooked in international climate discussions, in part because of the diversity of their characteristics. This diversity does make it difficult to assess the potential of urban policies to contribute to global climate goals.
With the recent increases in local urban data becoming available, however, our study shows that it is now possible to explicitly model and assess the consequences of climate strategies over a wide range of cities.
Important research gaps still remain. We could not, for instance, include any African cities in our sample due to challenges accessing reliable and comparable data. If current trends in data availability continue, this and other issues could be solved over the coming years.
The post Guest post: How 120 of the world’s major cities could cut transport CO2 by 22% appeared first on Carbon Brief.
Guest post: How 120 of the world’s major cities could cut transport CO2 by 22%
In the thick of the COP29 climate summit in Azerbaijan in 2024, the UN climate talks were rattled by what can only be described as a major PR disaster. The BBC, Reuters and The Guardian all carried headlines, attributed to leading climate policy experts, that the COPs were “no longer fit for purpose”.
The articles outlined a series of reforms called for in an open letter signed by 22 eminent scientists and politicians, including a former UN secretary-general and previous UN climate chief, with a further 150 lending their support. The headlines shook confidence in the COP process, just as governments were wrestling over a new climate finance goal.
The Club of Rome – which handled the media relations for the letter – hurried to say that its “constructive, supportive ideas” had been “misinterpreted”. Negotiators kept calm(ish) and carried on, in the end landing the finance goal after some high-stakes drama on the final day.
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To my surprise, when I went back this week to read the letter again, I could not find the offending line about the COPs not being fit for purpose. The Club of Rome has yet to respond to my query about its disappearance.
Whatever happened to the wording, that sentiment has been widely shared. COPs have ballooned in size while the importance of their outcomes seems to have diminished since the 2015 Paris Agreement (with the exception of the 2023 COP in Dubai where countries agreed to transition away from fossil fuels in energy systems).
The same on the surface
Two years on from those painful headlines in Baku, has anything changed for the better? You might be forgiven for thinking not. Official decisions are still made by consensus rather than the majority voting some have called for to stop blockers.
Tens of thousands of officials, activists and business execs still scurry around the halls to an ever-growing list of side events, roundtables and dialogues, while deals still come down to rows, all-nighters and jargon-filled texts adopted to rounds of applause.
But it would not be true to say that COPs have completely failed to respond to the very real need to translate the words of the Paris Agreement into action in the outside world.
Global warming is projected to be around 1.3C lower this century than it would have been if the world had not committed to tackle the climate crisis under that accord. Developing countries have a valued space at COPs in which their voices have equal weight in decision-making, unlike in many other international fora. And most importantly, perhaps, there has been a subtle shift, tipping the balance away from negotiating towards doing.
Brazil branded last year’s summit in Belém as the “COP of Implementation”, corralling the sprawling Action Agenda into six axes. This was a bid to impose some structure on the mushrooming efforts between governments, UN agencies, cities, businesses and civil society to set targets and spur faster results on their pet issues, from methane emissions to health and adaptation in conflict zones. COP30 alone saw the launch of 120 “plans to accelerate solutions”.
COP30 roadmaps off the cuff
Meanwhile, as the formal negotiations drew to a close, it was clear that consensus decision-making was evolving into something a little more improvised.
With only around half of all countries on board with the idea of a roadmap to transition away from fossil fuels, COP30 President André Corrêa do Lago announced his team would put one together over the coming year, along with another on how to meet a global goal to halt deforestation by 2030. Those roadmaps will be launched next week, presented and discussed at COP31, though it’s still unclear whether or how they’ll be incorporated into the formal negotiating agenda.
Some leading policy-makers don’t think that matters too much. Speaking to journalists before the Antalya summit, COP30 CEO Ana Toni and Dutch climate minister Stientje van Veldhoven said “coalitions of the willing” can move ahead without needing consensus from the COPs. This, they said, was evident this year at the first global conference on TAFF, co-chaired by van Veldhoven and attended by 60 countries.
“Consensus or no-consensus in the general COP doesn’t make a difference for the choices I have to make in my country to get my country to phase out fossil fuels,” said the Dutch minister. The Netherlands recently became one of the first to publish a national TAFF plan.
COP31 banks on flagship voluntary initiatives
This thinking has permeated the management and expected outcomes of this year’s COP too. Earlier this year, Türkiye, supported by international energy agencies, floated the idea of a voluntary goal to boost electrification to 35% of the world’s final energy consumption by 2035 – and this is now being touted as one of the main results to be expected from Antalya.
Türkiye is also championing a pledge on AI and climate, while co-host Australia is pushing to ease access to climate finance for least developed countries and small island states.
COP31 presidency announces AI pledge as UN climate chief says Big Tech ‘on thin ice’
None of these needs consensus. But with a political cover decision already in the works, as trailed by the COP presidents, they – and perhaps the fossil fuel roadmap – may find a home in the official text if language acceptable to most can be found, giving them them additional weight.
UNFCCC reform process in the shadows
Formal reform is underway too, if quietly. UN climate chief Simon Stiell is leading a review informed by ongoing consultations with a group of 15 well-respected climate policy experts, three of whom signed the open letter in 2024.
Among them is leading Swedish climate and sustainability scientist Johan Rockström who has strong ideas about how to make COPs function better, including a switch to majority voting. He told the same press briefing nothing stands in the way of this, because the rules of procedure for making decisions at COPs have never been formally agreed.
Still, to get away from the default setting of consensus would require agreement on a new system that may be impossible to achieve given the rise in bullying tactics by fossil fuel heavyweights.
Comment: The UN climate process was built for negotiation – now it must support implementation
The deliberations with the high-level policy gurus, as reflected in a summary of June’s session in Bonn, largely echo what’s already happening organically, calling for stronger partnerships and accountability both in and between the Action Agenda and negotiations. It doesn’t mention voting.
A general overview of the reform exercise says that “improving and optimizing the [UN climate] process over the medium to long term… will be critical to fostering trust, enhancing collaboration, and catalyzing increased ambition”.
In the short term, don’t hold your breath for anything concrete on reform at COP31 but watch for signs in what ends up dominating the headlines from Türkiye.
The post Editor’s Desk: COP reform is happening quietly, behind the headlines appeared first on Climate Home News.
Editor’s Desk: COP reform is happening quietly, behind the headlines
With the COP31 climate summit in Turkey looming, all eyes are on China to see what the country will push for in the negotiations.
At COP30 last year, China helped to secure a “dialogue” on climate-related “unilateral trade measures”, as well as a two-year “work programme” concerning climate finance.
The nation also championed south-south cooperation throughout the conference and co-led a summit on methane, alongside Brazil and the UK.
In a recent press conference, China’s environment vice-minister Li Gao noted the need to “uphold multilateralism” and send a “clear political signal” that the global community is united around climate action.